1. Field of the Invention
The present invention relates to a media access control (MAC) algorithm containing two modes, and a method for using the same. Specifically, the present invention relates to a MAC algorithm with separate operation modes for good channel and bad channel communication in a communication network, such as a wireless ad-hoc communication network. In each mode, the MAC algorithm is configured to vary operational parameters, including channel vector values transmitted in request-to-send/clear-to-send (RTS/CTS) messages, depending on the channel mode indicated.
2. Description of the Related Art
Wireless communications networks, such as mobile wireless telephone networks, have become increasingly prevalent over the past decade. These wireless communications networks are commonly referred to as xe2x80x9ccellular networksxe2x80x9d, because the network infrastructure is arranged to divide the service area into a plurality of regions called xe2x80x9ccellsxe2x80x9d. A terrestrial cellular network includes a plurality of interconnected base stations, or base nodes, that are distributed geographically at designated locations throughout the service area. Each base node includes one or more transceivers that are capable of transmitting and receiving electromagnetic signals, such as radio frequency (RF) communications signals, to and from mobile user nodes, such as wireless telephones, located within the coverage area. The communications signals include, for example, voice data that has been modulated according to a desired modulation technique and transmitted as data packets. As can be appreciated by one skilled in the art, network nodes transmit and receive data packet communications in a multiplexed format, such as time-division multiple access (TDMA) format, code-division multiple access (CDMA) format, or frequency-division multiple access (FDMA) format, which enables a single transceiver at the base node to communicate simultaneously with several mobile nodes in its coverage area.
In recent years, a type of mobile communications network known as an xe2x80x9cad-hocxe2x80x9d network has been developed for use by the military. In this type of network, each mobile node is capable of operating as a base station or router for other mobile nodes, thereby eliminating the need for a fixed infrastructure of base stations. Details of an ad-hoc network are set forth in U.S. Pat. No. 5,943,322 to Mayor, the entire content of which is incorporated herein by reference.
More sophisticated ad-hoc networks are also being developed which, in addition to enabling mobile nodes to communicate with each other as in a conventional ad-hoc network, further enable the mobile nodes to access a fixed network and communicate with other mobile nodes, such as those on the public switched telephone network (PSTN), and on other networks, such as the Internet. Details of these advanced types of ad-hoc networks are described in U.S. patent application Ser. No. 09/897,790 entitled xe2x80x9cAd Hoc Peer-to-Peer Mobile Radio Access System Interfaced to the PSTN and Cellular Networksxe2x80x9d, filed on Jun. 29, 2001, in U.S. patent application Ser. No. 09/815,157 entitled xe2x80x9cTime Division Protocol for an Ad-Hoc, Peer-to-Peer Radio Network Having Coordinating Channel Access to Shared Parallel Data Channels with Separate Reservation Channelxe2x80x9d, filed on Mar. 22, 2001, and in U.S. patent application Ser. No. 09/815,164 entitled xe2x80x9cPrioritized-Routing for an Ad-Hoc, Peer-to-Peer, Mobile Radio Access Systemxe2x80x9d, filed on Mar. 22, 2001, the entire content of each being incorporated herein by reference.
Communication between nodes, however, is often subject to interference and transmission errors. To minimize the occurrence of erroneous data, receivers and transmitters may be configured to detect transmission errors in a number of ways and if detected, request retransmissions. For instance, a data transmission system between nodes may include an automatic repeat request (ARQ) transmitter and receiver, each adapted to use an error correction code. As may be appreciated by one skilled in the art, the ARQ transmitter may be used to include error detection codes in the transmission data stream to a remote receiver. The ARQ receiver may then be used to detect errors in the data stream using such codes and request retransmission from the transmitter. Further details of ARQ application and use of error detection codes may be found in U.S. Pat. No. 5,629,948 to Hagiwara et al., and in U.S. Pat. No. 5,784,362 to Turina, the entire content of each being incorporated herein by reference. The selective use of ARQ with a sliding window transport mechanism is also discussed in U.S. Pat. No. 5,717,689 to Ayanoglu, and still another ARQ retransmission technique using a xe2x80x9cgo-back-nxe2x80x9d ARQ command is discussed in U.S. Pat. No. 4,726,027 to Nakamura et al., the entire content of each being incorporated herein by reference.
However, ARQ media access control (MAC) for ad-hoc networks encounter several difficulties. As known to those skilled in the art, data packet collisions can occur if transmissions overlap. In such cases, an ACK will not be received and both packets must be retransmitted. As noted in an article by Garcia-Luna-Aceves et al., entitled xe2x80x9cReversing The Collision-Avoidance Handshake In Wireless Networksxe2x80x9d, the entire content of which being incorporated herein by reference, one solution to packet collisions involves split-channel reservation multiple access (SRMA) wherein a node requiring to transmit data to a receiver first sends a request-to-send (RTS) packet to the receiver, who responds with a clear-to-send (CTS) packet if it receives the RTS correctly. However, multichannel MAC design, which is basically an extension of multiple access with collision avoidance (MACA) algorithm, typically cannot efficiently handle such ARQ functions. Additional details of the MACA algorithm is presented in an article by Phil Karn, entitled xe2x80x9cMACA-A New Channel Access Method For Packet Radioxe2x80x9d, and in an article by Tang et al., entitled xe2x80x9cCollision-Avoidance Transmission Scheduling For Ad-Hoc Networksxe2x80x9d, the entire content of each being incorporated herein by reference.
Where retransmissions are required, the MACA algorithm handles ARQ by repeating the whole request to send/clear to send channel access sequence. This includes transmission of an entire channel vector, equal to the length of channel reservation. This is inefficient in some channel conditions due to fact that resend will happen with a very high probability. Accordingly, a need exists for an ARQ MAC that can handle ARQ segment retransmissions more efficiently.
An object of the present invention is to provide a system and method of media access control (MAC) which handles ARQ segment retransmissions more efficiently in ad-hoc communication networks.
Another object of the present invention is to provide a system and method for estimating a channel vector length is a first mode of operation, and communicating the length to a first group of nodes for use in RTS/CTS sequences.
Another object of the present invention is to provide a system and method for monitoring a data channel to determine an actual channel vector length, and communicating the actual length to a first group of nodes for use in RTS/CTS sequences.
Still another object of the present invention is to provide a system and method for a second mode of operation, wherein the true channel vector is communicated to a first group of nodes for use in RTS/CTS sequences.
These and other objects are substantially achieved by providing a system and method for a MAC algorithm with separate operation modes. Individual operation modes can be created based on channel specifics, including a separate mode for good channel and bad channel communication. For each mode, channel vector values transmitted during collision avoidance operations, such as in an exchange of request-to-send/clear-to-send (RTS/CTS) messages, are varied depending on channel mode, thus resulting in optimized system throughput.
In a first mode, the present invention provides a system and method to estimate a channel vector length, and communicate the length to a first node, and an associated group of nodes receiving the RTS/CTS sequence. Each node then maintains this channel length for use in their own RTS/CTS sequences. Additionally, the data channel is monitored in the case of bad channels, to determine an actual channel vector length by monitoring partial and complete acknowledgement (ACK) messages. Once the actual channel vector length is determined, it can be communicated to the associated group of nodes directly, in the case of individual RTS/CTS sequences, or as a group, in the case where the nodes monitor adjacent RTS/CTS sequences. In a second mode, a maximum channel vector length is used, as retransmissions are less probable in good channels.
Specifically, in good channel operation mode, the true channel vector is communicated in the RTS/CTS and used. In bad channel operation mode, the estimated channel vector is communicated in the RTS/CTS and used, however the data channel is monitored for partial and complete ACK messages to detect the actual channel vector. This actual channel vector is then communicated in the RTS/CTS and used, and provided to other nodes to update channel vector information.